This application is a national stage of PCT/EP99/00436 filed Jan. 23, 1999 and based upon German national application 198 04 415.1 filed Feb. 5, 1998 under the International Convention.
The invention relates to a method and to a device for shortening the splice tail resulting from a flying roll change.
Continuously working paper processing machines, particularly rotary web-fed machines, are fed with paper webs which are unwound from rolls. When a roll is finished, it is replaced by a new roll without stopping the processing machine. Roll changers are known which work with a so-called xe2x80x9cflying roll exchangexe2x80x9d. The initial portion (leading end) of a new roll in stand-by position is first provided with an adhesive point. Then the new roll is set into rotation and brought to a peripheral speed which is synchronized with the speed of the web reeling off the almost empty roll. At the right moment the unwinding web is pressed against the new roll, so that it touches the same in the area of the adhesive point. The initial portion of the new web is thus glued to the reeling-off web. The reeling-off web is cutoff shortly behind of the splicing point.
According to DE 26 19 236 C3 which describes a roll changer with the pertaining control system, the segment of the old web defined as the so-called xe2x80x9csplice tailxe2x80x9d should have a predetermined length from the adhesive point to the separated end so that when the splice tail passes through the printing machine no disturbances occur.
However it has been found that the tails cause disturbances in the subsequent processing stations even when they all are of equal, prescribed lengths. Since the cut always occurs with a delay due to the inert mass of the cutting device and to the cycle timing of the control system, the tail cannot be cut off as short as desired. If for instance the delay time is 10 ms and the web speed is 15 m/s, then the tail is at least 150 mm long.
According to the DE 29 11 268 A1, which describes a similar roll changer, during the nonstop unwinding of the webs of material the tendency is to keep the tail as short as possible, since it can be damaging to further processing. According to the cited reference this problem is solved by arranging on the new roll behind the adhesive area a rip cord provided with an entrainment element. The latter remains attached to the pressure roller when the paper web is pressed against the new roll and activates the rip cord, so that it separates the paper web. This makes it possible to glue the reeling-off paper web to a new paper web without a splice tail.
However it has proven in practice that the efforts of the roll preparation, as well as the control of the rip cord after adhesion cause considerable expense, so that this method has not been validated.
Starting from the idea that the formation of a troublesome tail can be hardly avoided with present technical means, it is the object of the invention to provide a method which will shorten the tail to an acceptable length, before it reaches the downstream processing stations. It is also an object to provide a suitable device for the implementation of the method.
This object is achieved in a method of shortening the splice tail following a flying roller change, whereby a running paper web is taken up from a roll approaching its end and fed to a processing station, pressed against the glue-covered initial portion (leading end) of a new roll synchronized with the travelling paper web and subsequently trimmed after a short interval. According to the invention, the paper web is guided through a curved portion of a path, whose center lies on the side of the web facing away from the tail so that the tail raised by the centrifugal force is cut off close to the curved portion. Between the paper web and the tail an air blast can be blown in the direction of the web travel. Due to suction the tail can adhere to the side facing away from the center of the curvature. The tail can be braked due to friction with a surface at rest or moving slower than the paper web. The tail can be accelerated by a frictional locking with a surface moving faster than the paper web.
The device for shortening the splice tail is located downstream of an unwinding device which is equipped with means for flying roll exchange, wherein a passing paper web taken up from a roll approaching its end and fed to a processing station is pressed against the glue-covered initial portion of a new roll synchronized with the paper web and is subsequently trimmed after a short time interval. This device is characterized by a guide roller and a knife arranged at a short distance from the shell surface of the guide roller. The blade of the knife is serrated. At a distance from the blade of the knife at least one blast nozzle is arranged and can have blast openings for blowing an air blast in the running direction of the paper web. A suction box with a suction slot can be located in the immediate vicinity of the blade of the knife. Upstream of the blade of the knife, at a distance from the paper web, a suction belt can be arranged which runs approximately tangentially to the guide roller. The suction belt can revolves at a speed which is higher than the peripheral speed of the guide roller. Upstream of the blade of the knife, at a distance from the guide roller a cylinder can be arranged parallel thereto. The shell of the cylinder can be provided with a friction-enhancing coating. The shell of the cylinder can be is perforated and the interior of the cylinder can be connected to a suction device. Two guide roller can be provided, between which the paper web runs through a rectilinear portion. A suction box with a perforated suction wall can be located at a distance from and oppositely to the paper web covering the length of the rectilinear portion, and by a knife, can be arranged at a short distance from the subsequent guide roller.